- Operating frequency is not appropriate for the location
To fix interference on a mic, you need to adjust the frequency on the mic and receiver to another frequency that is not in use. You have to change it at least 2 MHz up or down from where you were having interference. Mostly, you just have to play with it in order to find what the best frequencies are in your area. You can also use a wireless frequency analysis program, but those are expensive, and require expensive hardware.
Intermodulation is similar to interference. Intermodulation happens when you have two microphones or other wireless devices crowding each other frequencies. The only way to fix this is to change your frequencies to another frequency that is not crowded.
- Local interference from other electronic devices or wireless systems
How to check: Turn off electronic devices that are within 5 feet of the wireless receiver, such as a DVD player, a CD player, a computer, an iPod, the transmitter for an in-ear monitor system. Or remove the wireless system and take it to a different location that is at least ½ mile away. If it works OK there, the problem is local interference in the original location. Finding the exact source of local interference often requires the use of a frequency spectrum analyzer - an expensive piece of test equipment.
- Signal Blockage
One of the most common problems with wireless systems is signal blockage. Walls, metal, even the human body can affect signals. There isn't too much you can do about signal blockage, except trying to move your receivers around trying to find a good spot that is not blocked. Also, make sure that antennas are not touching a person's skin. The human body acts as an antenna, absorbing signal.